1. Field of the Invention
The present invention relates to a technique which transmits and receives data in a communication system, and more particularly, relates to a technique which transmits and receives data in a broadband radio access system.
2. Description of the Related Art
As the transmission rate of a communication system becomes faster, the transmission capacity (band, delay) of a backhaul network through which a node such as a radio base station, DSLAM (Digital Subscriber Line Access Multiplexer) or MSAN (Multi-Service Access Node) connects to a core network comes to influence the performance of the entire network. While voice communication only requires lease of a few dedicated lines of 1.5 Mbps (Megabit per second) or 2 Mbps, broadband communication cannot be accommodated by that and requires many dedicated lines. Accordingly, the use of dedicated lines in broadband communication system raises running costs, adversely affecting business of communications carriers. It is difficult to secure large transmission capacity for broadband access due to constraints of the frequency band, the channel band and the like which can be used even when a backhaul is constructed using microwave communication devices which communicate in a point-to-point fashion without dedicated lines.
Typically, these microwave communication devices transparently transmit every signal from a BS (Base Station). However, according to this, redundant data may be intermingled in traffic, thereby reducing transmission efficiency.
In particular, since a backhaul from a BS to a core network which is used for broadband access requires a wide band to be secured, construction of an economical network requires transmission without waste.
In order to improve transmission efficiency, for example, a technique disclosed in Japanese Patent Laid-Open No. 2002-124916 (hereinafter referred to as Patent Document 1) increases resources by using a combination of radio bands different from each other in terms of uplink and downlink.
Japanese Patent Laid-Open Nos. 2006-197605 and 2007-135206, and National Publication of International Patent Application No. 2007-524330 (hereinafter referred to as Patent Documents 2 to 4, respectively) disclose techniques which dynamically change backhaul resources. National Publication of International Patent Application No. 2004-503176 (hereinafter referred to as Patent Document 5) discloses a technique which changes a parameter for setting quality of service to be secured.
However, the techniques that are described in Patent Documents 1 to 4, while improving the transmission efficiency by increasing the resources, require costs for increasing the resources.
On the other hand, while the technique that are described in Patent Document 5 accommodates the increase of traffic by changing the quality of service, it is impossible to improve the transmission efficiency with the changed quality of service.
Thus, according to the techniques that are described in Patent Documents 1 to 5, there are problems in that it is difficult to improve the transmission efficiency while restricting increase in cost.